Resting AC directly on top of ductwork

[Ian Gills]

I note in my house that while most of the BX/AC/MC has been pulled through small holes in the joists a significant section (4-5 feet) of the circuit for the furnace rests directly on top of the furnace duct work which hangs slightly below the joists above. Is it allowed to suport AC on ductwork like this?

It seems like a no-no to me, but I would like some opinions before I contact an electrician to properly route the cable through freshly cut holes in the joists.

[Greg Fretwell]

MC only has to be supported every 6 feet. If you are worried about it vibrating and making noise in the ducts, have him put up a running board and strap it to that. Accessibility may be an issue here.

[Ian Gills]

Thanks Greg. It just seems strange that the cable is resting on top of the ductwork.

[brian winkle]

Greg, ever wonder why article 220 (AC) requires support every 4.5 feet and article 230 (MC) only requires it every 6 feet?

[Paul W. Abernathy]

Probably because it was increased with a proposal in the past and no one submitted it for both ..

One arguement could be made that since AC uses the outside metal jacket as the EGC and with MC it has a internal EGC....running AC without proper support could mean the AC could be damaged if alowed to sag.....possibly effecting the EGC properties.....hey just my guesses only......

And since AC can extend to 6' to lumnaires from the last support in a accessible ceiling is ok because it will technically lay on the grid...which is allowed.........

Hey.....just me talking out loud fella.....lol